With an increase in capacity of information processing in recent years, various information recording technologies have been developed. In particular, the surface recording density of an HDD using magnetic recording technology is continuously increasing at an annual rate of approximately 100%. In recent years, an information recording capacity exceeding 160 GB per one magnetic disk with a 2.5-inch diameter for use in an HDD or the like has been desired. To fulfill such demands, an information recording density exceeding 250 Gbits per one square inch is desired to be achieved.
To attain a high recording density in a magnetic disk for use in an HDD or the like, a magnetic disk of a perpendicular magnetic recording type has been suggested in recent years. In a conventional in-plane magnetic recording type, the axis of easy magnetization of a magnetic recording layer is oriented in a plane direction of a base surface. In the perpendicular magnetic recording type, by contrast, the axis of easy magnetization is adjusted so as to be oriented in a direction perpendicular to the base surface. In the perpendicular magnetic recording type, compared with the in-plane recording type, the demagnetizing field (Hd) increases as magnetic particles are finer to improve a coercivity Hc, thereby allowing a heat fluctuation phenomenon to be suppressed. Therefore, the perpendicular magnetic recording type is suitable for increasing recording density.
A conventional magnetic disk for magnetic recording is configured of a substrate made of aluminum, glass, or the like, a magnetic recording layer for magnetic recording, and a carbon-made medium protective layer (carbon protective layer) and a lubricating layer for the purpose of ensuring reliability of the magnetic disk.
In recent years, with an increase in recording density, the floating amount between the magnetic head and the disk decreases. For example, as one technique for stabilizing the control of the floating amount of the magnetic head and achieving a further decrease of the floating amount, a technique called DFH (Dynamic Flying Height) has been developed (for example, Non-Patent Document 1). According to DFH, a heater element is embedded in a magnetic head, and the heater element is caused to generate heat at the time of operation of the magnetic head. With that heat, the magnetic head thermally expands to slightly protrude toward the magnetic disk. With this, only at that moment, a magnetic spacing, which is a magnetic gap, between the magnetic head and the main surface of the magnetic disk can be decreased. That is, DFH is a technology capable of decreasing the floating amount of the magnetic head from the magnetic disk.
With this DFH head, a further decrease of the floating amount can be achieved. However, the magnetic head has an MR element mounted thereon, which disadvantageously causes a head crush failure or a thermal asperity failure as a unique failure. Also, even when these failures are not caused, intermittent contacts between the magnetic head and the disk are assumed to increase in the future.
For this reason, demands for decreasing the coefficient of friction of the surface of the lubricating layer have increased. This is because, when a contact occurs, it is desired to decrease a damage to the magnetic head and the disk to improve durability and also to decrease wear of the carbon-made medium protective layer even if only slightly.
In addition, typically in the case of mounting (vehicle-mounting) on a passenger automobile, the environment where an HDD device is adopted has also become extremely severe, such as high temperatures and humidity. Under this environment, contamination of the disk is serious, and it is important to take measures for a highly-active carbon protective layer.    Non-Patent Document 1: Myokan, “2.5-inch Hard Disk Drives for Mobile Equipment”, magazine FUJITSU, Volume 58, No. 1, pp. 10-15, FUJITSU Limited, January 2007.